Losing the Arms Race: Greater Wax Moths Sense but Ignore Bee Alarm Pheromones

The greater wax moth, Galleria mellonella (L.) uses two different sensory modalities to evaluate the suitability of potential oviposition sites

An ovipositing insect evaluates the benefits and risks associated with the selection of an oviposition site for optimizing the fitness and survival of its offspring. The greater wax moth, Galleria mellonella (L.), uses beehives as an oviposition site. During egg-laying, the gravid wax moth confronts two kinds of risks, namely, bees and conspecific larvae. While bees are known to attack the moth's offspring and remove them from the hive, the conspecific larvae compete for resources with the new offspring. To date, little is known about the mechanisms involved in the assessment of oviposition site by the greater wax moth, G. mellonella (L.). Here, we demonstrate that the wax moth uses two different sensory modalities to detect risks to its offspring in the hives of Apis cerena. Bees appear to be detected by the contact-chemoreception system of the gravid wax moth, while detection of conspecifics relies on the olfactory system. Hence, our findings suggest that two different sensory modalities are used to detect two different risks to the offspring and that the selection of oviposition sites by G. mellonella (L.) relies on the integration of inputs from both the olfactory and contact-chemoreception systems.

Identification of Olfactory Genes From the Greater Wax Moth by Antennal Transcriptome Analysis

The olfactory system is used by insects to find hosts, mates, and oviposition sites. Insects have different types of olfactory proteins, including odorant-binding proteins (OBPs), chemosensory proteins (CSPs), odorant receptors (ORs), ionotropic receptors (IRs), and sensory neuron membrane proteins (SNMPs) to perceive chemical cues from the environment. The greater wax moth, Galleria mellonella, is an important lepidopteran pest of apiculture. However, the molecular mechanism underlying odorant perception in this species is unclear. In this study, we performed transcriptome sequencing of G. mellonella antennae to identify genes involved in olfaction. A total of 42,544 unigenes were obtained by assembling the transcriptome. Functional classification of these unigenes was determined by searching against the Gene Ontology (GO), eukaryotic orthologous groups (KOG), and the Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. We identified a total of 102 olfactory-related genes: 21 OBPs, 18 CSPs, 43 ORs, 18 IRs, and 2 SNMPs. Results from BLASTX best hit and phylogenetic analyses showed that most of the genes had a close relationship with orthologs from other Lepidoptera species. A large number of OBPs and CSPs were tandemly arrayed in the genomic scaffolds and formed gene clusters. Reverse transcription-quantitative PCR results showed that GmelOBP19 and GmelOR47 are mainly expressed in male antennae. This work provides a transcriptome resource for olfactory genes in G. mellonella, and the findings pave the way for studying the function of these genes.

Honey Bee Alarm Pheromone Mediates Communication in Plant-Pollinator-Predator Interactions

Honey bees play a crucial role in pollination, and in performing this critical function, face numerous threats from predators and parasites during foraging and homing trips. Back in the nest, their defensive behavior drives some individuals to sacrifice themselves while fighting intruders with their stingers or mandibles. During these intense conflicts, bees release alarm pheromone to rapidly communicate with other nest mates about the present danger. However, we still know little about why and how alarm pheromone is used in plant–pollinator–predator interactions. Here, we review the history of previously detected bee alarm pheromones and the current state of the chemical analyses. More new components and functions have been confirmed in honey bee alarm pheromone. Then, we ask how important the alarm pheromones are in intra- and/or inter-species communication. Some plants even adopt mimicry systems to attract either the pollinators themselves or their predators for pollination via alarm pheromone. Pheromones are honest signals that evolved in one species and can be one of the main driving factors affecting co-evolution in plant–pollinator–predator interactions. Our review intends to stimulate new studies on the neuronal, molecular, behavioral, and evolutionary levels in order to understand how alarm pheromone mediates communication in plant–pollinator–predator interactions.